Gas turbine engine with intercooled cooling air and dual towershaft accessory gearbox

Abstract

An exemplary gas turbine engine assembly includes a fan section including a fan, a first spool having a first turbine operatively mounted to a first turbine shaft, and a second spool having a second turbine operatively mounted to a second turbine shaft. The first and second towershafts are respectively coupled to the first and second turbine shafts. An accessory drive gearbox includes a set of gears. A compressor is driven by the first towershaft. A transmission couples a starter generator assembly to the set of gears. The transmission is transitionable between a first mode where the starter generator assembly is driven at a first speed relative to the second towershaft in response to rotation of the second towershaft, and a second mode where the starter generator assembly is driven at a different, second speed relative to the second towershaft in response to rotation of the second towershaft.

What is claimed is: 
     
       1. A gas turbine engine assembly comprising:
 a fan section including a fan, and an outer housing that surrounds the fan to establish a bypass duct, wherein the fan section drives air along a bypass flow path in the bypass duct; 
 a first spool having a first turbine operatively mounted to a first turbine shaft; 
 
       a second spool having a second turbine operatively mounted to a second turbine shaft, the first and second turbines mounted for rotation about a common rotational axis within an engine static structure, the first and second turbine shafts coaxial with one another;
 first and second towershafts respectively coupled to the first and second turbine shafts; 
 an accessory drive gearbox with a set of gears; 
 a compressor driven by the first towershaft; 
 a starter generator assembly; and 
 a transmission coupling the starter generator assembly to the set of gears, the transmission transitionable between a first mode where the starter generator assembly is driven at a first speed relative to the second towershaft in response to rotation of the second towershaft, and a second mode where the starter generator assembly is driven at a different, second speed relative to the second towershaft in response to rotation of the second towershaft. 
 
     
     
       2. The gas turbine engine assembly of  claim 1 , wherein the first and second turbine shafts are outer and inner shafts, respectively, and the first and second turbines are high and low pressure turbines, respectively. 
     
     
       3. The gas turbine engine assembly of  claim 2 , wherein the first towershaft is configured to rotate at a higher speed than the second towershaft. 
     
     
       4. The gas turbine engine assembly of  claim 3 , wherein the inner shaft interconnects the low pressure turbine and the fan. 
     
     
       5. The gas turbine engine assembly of  claim 4 , wherein the fan is driven by the second turbine through a geared architecture. 
     
     
       6. The gas turbine engine assembly of  claim 1 , further comprising:
 a first clutch disposed between the first towershaft and the starter generator assembly, the first clutch configured to enable the starter generator assembly to drive the first spool through the accessory drive gearbox; and 
 a second clutch disposed between the second towershaft and the starter generator assembly, the second clutch configured to enable the second spool to drive the starter generator assembly through the accessory drive gearbox. 
 
     
     
       7. The gas turbine engine assembly of  claim 6 , further comprising:
 a compressor section including a low pressure compressor and a high pressure compressor, the high pressure compressor driven by the first turbine; 
 wherein the first and second turbine shafts are outer and inner shafts, respectively, and the first and second turbines are high and low pressure turbines, respectively; and 
 wherein the first towershaft is configured to rotate at a higher speed than the second towershaft. 
 
     
     
       8. The gas turbine engine assembly of  claim 7 , wherein the fan is driven by the second turbine through a geared architecture. 
     
     
       9. The gas turbine engine assembly of  claim 8 , wherein a bypass ratio is defined as the volume of air passing into the bypass duct compared to the volume of air passing into the compressor section, and the bypass ratio is greater than 10. 
     
     
       10. The gas turbine engine assembly of  claim 9 , wherein the geared architecture is an epicyclic gear train. 
     
     
       11. The gas turbine engine assembly of  claim 10 , the compressor is a boost compressor of an intercooled cooling air system. 
     
     
       12. The gas turbine engine assembly of  claim 11 , wherein the compressor section has a downstream most end and a cooling air tap at a location spaced upstream from the downstream most end, wherein the cooling air tap is passed through the boost compressor and at least one heat exchanger, and then passed to a turbine section to cool the turbine section, and wherein the turbine section comprises the high and low pressure turbines. 
     
     
       13. The gas turbine engine assembly of  claim 12 , wherein the low pressure compressor is driven by the low pressure turbine. 
     
     
       14. The gas turbine engine assembly of  claim 13 , wherein the first clutch and the second clutch are one-way mechanical clutch devices. 
     
     
       15. The gas turbine engine assembly of  claim 6 , wherein the first clutch and the second clutch are one-way mechanical clutch devices. 
     
     
       16. The gas turbine engine assembly of  claim 1 , wherein the compressor is a boost compressor of an intercooled cooling air system. 
     
     
       17. The gas turbine engine assembly of  claim 16 , further comprising a compressor section having a downstream most end and a cooling air tap at a location spaced upstream from said downstream most end, and wherein the cooling air tap is passed through at least one boost compressor and at least one heat exchanger, and then passed to a turbine section to cool the turbine section. 
     
     
       18. The gas turbine engine assembly of  claim 1 , wherein the fan is driven by a speed reduction device, and the speed reduction device is driven by the second turbine shaft. 
     
     
       19. The gas turbine engine assembly of  claim 1 , wherein the starter generator assembly comprises a first variable frequency generator and a second variable frequency generator. 
     
     
       20. The gas turbine engine assembly of  claim 1 , wherein the starter generator assembly comprises a first integrated drive generator and a second integrated drive generator. 
     
     
       21. The gas turbine engine assembly of  claim 8 , wherein the transmission and the set of gears are separate and distinct components. 
     
     
       22. The gas turbine engine assembly of  claim 21 , wherein the fan is axially forward of the high and low pressure compressors relative to an engine longitudinal axis, and the high and low pressure compressors are axially forward of the high and low pressure turbines relative to the engine longitudinal axis. 
     
     
       23. The gas turbine engine assembly of  claim 22 , wherein:
 the geared architecture is an epicyclic gear train; and 
 the epicyclic gear train is axially forward of the high and low pressure compressors, but is axially aft of the fan, relative to the engine longitudinal axis. 
 
     
     
       24. The gas turbine engine assembly of  claim 21 , further comprising:
 a splitter that divides airflow from the fan between the bypass duct and an entrance of the compressor section, the splitter axially aft of the fan relative to the engine longitudinal axis.